Multiplication and Division, Part 1

Lesson 8

Objective

Build fluency with division facts using units of 2, 5, and 10.

Materials and Resources

Common Core Standards

Core Standards

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  • 3.OA.A.2 — Interpret whole-number quotients of whole numbers, e.g., interpret 56 ÷ 8 as the number of objects in each share when 56 objects are partitioned equally into 8 shares, or as a number of shares when 56 objects are partitioned into equal shares of 8 objects each. For example, describe a context in which a number of shares or a number of groups can be expressed as 56 ÷ 8.

  • 3.OA.B.6 — Understand division as an unknown-factor problem. For example, find 32 ÷ 8 by finding the number that makes 32 when multiplied by 8.

  • 3.OA.C.7 — Fluently multiply and divide within 100, using strategies such as the relationship between multiplication and division (e.g., knowing that 8 × 5 = 40, one knows 40 ÷ 5 = 8) or properties of operations. By the end of Grade 3, know from memory all products of two one-digit numbers.

Criteria for Success

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  1. Solve division and unknown factor problems involving twos, fives, and tens by skip-counting, keeping track on their papers or on their fingers of how many twos, fives, or tens have been counted, stopping the skip-counting sequence when they reach the dividend, knowing that the number of twos, fives, or tens that they counted is the solution. 

Tips for Teachers

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  • “For $$8\times3$$, you know the number of 3s and count by 3 until you reach 8 of them. For $$24\div 3$$, you count by 3 until you hear 24, then look at your tracking method to see how many 3s you have. Because listening for 24 is easier than monitoring the tracking method for 8 3s to stop at 8, dividing can be easier than multiplying” when using a skip-counting strategy to solve (OA Progression, p. 25). Thus, this lesson should be more accessible to students than Lesson 7.
  • As a supplement to the Problem Set, students can play the first version of "What's your Number?" from the Preferred Tasks in 3.OA.4 - About the Math, Learning Targets, and Rigor by the Howard County Public School System.

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Anchor Tasks

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Problem 1

Maureen says the skip-counting sequence “10, 20, 30, 40, 50, 60” to help her solve a problem.

a. What multiplication problem might Maureen be trying to solve? How do you know? 

b. What if Maureen was solving a division problem? What problem might that have been? 

Guiding Questions

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Problem 2

Solve. 

a.   $$12\div2 =$$ _____

b.   _____ $$=35\div 5$$

c.   $$90\div 10=$$  _____

d.   _____ $$\times 5 = 45$$

e.   $$2 \times$$ _____ $$=16$$

Guiding Questions

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Discussion of Problem Set

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  • I think the answer in #3f is 8. Do you agree or disagree? What mistake did I make? 
  • What do you notice about #11a and #11d? What do you wonder? 
  • Is division commutative? How do you know? 

Target Task

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Solve.

1.   $$90 \div 10 =$$ _____                                    2.   ____ $$\times 2 = 8$$                                     3.   $$40 = 5\times $$ _____

Mastery Response

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